The present invention relates generally to the field of electrical circuit breakers, and more particularly to an interlock for at least two circuit breakers.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts:
the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range. The tripping mechanism may be housed in the same housing as the operating mechanism and contacts or it may be housed in a separate housing coupled to the housing containing the operating mechanism and contacts.
In many instances, several circuit breakers are used to control an electrical system. Often more than one circuit breaker is provided in order that one breaker will be operating while another is being serviced or replaced. Multiple circuit breakers are used typically to allow multiple power sources to be available for use as inputs to an electrical system without the hazard of both systems energized on the electrical system simultaneously. A common application of this type of arrangement is used as a transfer switch. The transfer switch controls the input power to an electrical system from the main power lines and a back-up power source such as a generator. The switch controls whether one of the power line or generator is connected to the electrical system to provide the input power. In such case, a separate circuit breaker would be used in each of the power source input lines. However, an operator would want only one circuit breaker operable in the overall system. Although some mechanical interlocking devices have been disclosed in the past for other types of circuit breakers, such interlock devices are designed to be used with specific circuit breakers or are installed in the circuit breaker housing, or require additional and complex circuitry to operate the interlock such as using an electrically energized relay.
Thus, there is a need for an interlock for circuit breakers that does not require additional circuitry or mechanisms to operate. There is a need for an interlock for circuit breakers which allows only one circuit breaker at a time to be energized. There is also a need for an interlock which the driving force to operate the interlock is provided by the circuit breakers themselves but also provides a neutral position when both circuit breakers are in the xe2x80x9coffxe2x80x9d position.
The present invention provides a method for preventing two circuit breakers from operating in the same electrical circuit, with each circuit breaker having a cross bar and contact assembly. The method comprises the steps of providing a first operator rod configured to engage the cross bar and contact assembly of one circuit breaker. Providing a second operator rod configured to engage the cross bar and contact assembly of the other circuit breaker. Providing an interlock yoke having two ends, with a notch proximate each end of the yoke. Mounting the yoke a spaced distance from the two circuit breakers. Pivoting the yoke a distance between the two circuit breakers and aligning each notch with one of the first and second operator rods. When one operator rod is moved by the cross bar and contact assembly of one circuit breaker, that operator rod pivots the yoke causing the other operator rod to block the operation of the other circuit breaker. Another embodiment of the method provides that the yoke is mounted on a structure apart from a circuit breaker supporting structure.
There is also provided an interlock for two circuit breakers, with the circuit breakers configured in the same electrical circuit and with each circuit breaker having a cross bar and contact assembly. The interlock comprises a pivot pin mounted a spaced distance from the two circuit breakers. An interlock yoke having two ends, with a notch proximate each end of the yoke and the yoke is coupled to the pivot pin. A first operator rod having a first end is configured to engage the cross bar and contact assembly of one circuit breaker and has a second end configured to engage the notch of the yoke. A second operator rod having a first end is configured to engage the cross bar and contact assembly of the other circuit breaker and has a second end configured to engage the notch of the yoke. When one operator rod is moved by the cross bar and contact assembly of one circuit breaker, that operator rod pivots the yoke, causing the other operator rod to block the operation of the other circuit breaker. Another embodiment of the interlock includes a locator member configured to align the operator rod with the cross bar and contact assembly of each respective circuit breaker. The locator member can also include a biasing member.
There is further provided an interlock for two circuit breakers with the circuit breakers configured in the same electrical circuit and with each circuit breaker having a cross bar and contact assembly. The interlock comprises a means for pivoting mounted a spaced distance from the two circuit breakers. A means for pushing having two ends, with a means for engaging proximate each end of the means for pushing and the means for pushing coupled to the means for pivoting. A first means for transmitting force having a first end configured to engage the cross bar and contact assembly of one circuit breaker and a second end configured to engage the means for engaging the means for pushing. A second means for transmitting force having a first end configured to engage the cross bar and contact assembly of the other circuit breaker and the second end configured to engage the means for engaging the means for pushing. When one means for transmitting force is moved by the cross bar and contact assembly of one circuit breaker that means for transmitting force pivots the means for pushing causing the other means for transmitting force to block the operation of the circuit breaker.